The present invention relates to a flexible disk cassette formed with a hollow housing of a relatively rigid material suitable for enclosing a thin flexible data storage or recording disk mounted for rotation within the housing. More particularly, the invention relates to such a disk cassette that includes means for stabilizing the motion of the flexible disk as the latter is rotated within the housing. The invention also relates to a disk having a novel hub or center plate structure, and a novel method of attaching the hub to the flexible disk.
Magnetic flexible or floppy disks are widely used as data storage media for computers because of their ease of handling and their relatively low cost. A floppy disk is a flexible disk, usually made of polyester resin and coated on both sides with a layer of a recording medium in which digital information can be recorded and/or retrieved by a read/write head or heads as the flexible disk is rotated by a disk drive.
While the present invention is primarily directed to magnetic recording disks, it should be understood that the inventive concepts described herein may be applied to other types of flexible disk cassettes wherein the disk recording medium embodies other recording techniques such as optical or magneto-optical recording.
Floppy disks of 51/4 inches or 8 inch diameter currently are contained in a flexible jacket formed with generally rectangular slots which serve as read/write head access windows, and with a center opening for engagement of the disk with a disk drive spindle. Presently there is a trend toward using microdisks that are 31/2 inches in diameter. These latter disks are packaged in cassettes and usually are designed to provide a higher recording density. However, the increased recording density also substantially increases the disk cassette's vulnerability to drop out (i.e loss of data usually due to inability of the head to read from or write onto the disk) caused by disk instability at the head/medium interface (e.g. disk vibration or flutter) that may vary the intended head to disk spacing. This condition is particularly pronounced at disk rotation speed in excess, for example of about 600 rpm, that are desirable to increase data transfer rates.
Some existing designs provide a measure of contaminant protection to these smaller diameter microdisks by packaging them in a cassette or enclosure that is more rigid or durable than the traditional 51/4 inch or 8 inch floppy disk jacket. In addition, a displaceable shutter may be provided to keep dust and foreign matter from entering the enclosure through the magnetic head access windows when the cassette is not in a disk drive. These newer cassettes usually include flexible wiping liners or cleaning sheets often made of nonwoven material adhered to the inside of both halves of the jacket or enclosure to wipe any debris from the floppy disk as it is rotated by the disk drive. These liners also prevent abrading or wearing of the floppy disk by inside surfaces of the hard floppy disk enclosure. In such known designs, however, the nonwoven material may be torn by irregularities and burrs on the outer edge of the rotating disk, resulting in damage the material and production of debris.
For example, U.S. Pat. No. 4,445,155 discloses a magnetic disk cassette enclosing a floppy disk protected adjacent each recording face by a sheet of nonwoven fabric welded to the inside of the cover, the fabric serving to clean the recording surface. A similar structure is shown in U.S. Pat. Nos. 4,517,617 and 4,510,546.
The designs disclosed in the above-identified Letters Patents appear to have limited data density storage capacities and limited speeds for disk rotation, distinct disadvantages, believed in part, to be a result of insufficient stabilization, i.e. minimization of motion or flutter of the disk transversely to its mean plane of rotation, particularly at the head/medium interface, as the disk is rotated within the cassette at high angular velocities by the disk drive.
Some minor degree of stabilization has been achieved, as described in commonly assigned copending U.S. patent application Ser. No. 781,060 filed Sept. 27, 1985 by providing, on interior surfaces of the cassette covers, radially extending tapered ribs, angularly spaced apart and alternately interdigitated from cover to cover. Other designs have been suggested to provide stabilization for floppy disks in cassettes.
For example, U.S. Pat. No. 4,301,486 issued Nov. 17, 1981 to S. H. Brown, et al discloses a recording cartridge containing a floppy disk, at least one side of which is coated with a magnetic flux-responsive material. One of the walls of the cartridge contains an access slot for a magnetic reading head. Disposed about the access slot is a raised portion having a large radius of curvature relative to the size of the disk. The raised portion is provided to cause the disk, upon rotation, to conform to the curvature thereby adding stability to the disk to maintain appropriate head-to-disk contact, and also to cause the disk to conform more readily to the curvature of the head for more effective transfer of information signals. The opposite surface of the interior of the cartridge is provided with a plurality of hump-shaped members which are alleged to exert aerodynamic pressure on the opposite side of the disk to bias it toward the magnetic head. These hump-shaped members are coated with conductive material so that upon direct contact with the underside of the disk, they drain off electrostatic charge during system operation. No provision is made to provide any cleaning sheets for the recording surface.
In U.S. Pat. No. 3,975,768 issued Aug. 17, 1976 to J. O. Jacques, et al., there is shown a cartridge containing a disk. The inside bottom of the cartridge has radially extending and circumferentially spaced ribs as well as circumferentially extended rib segments, all to assist in causing the disk to fly within the apparatus on an air film between the bottom of the cartridge and a head plate having a number of read/write transducers. No cleaning liner sheet is disposed adjacent the recording surface of the disk.
A principal object of the present invention is to provde a flexible disk cassette that allows the disk to be rotated at high speed and yet remain stabilized with respect to its intended mean plane of rotation.
A further object of the present invention is to provide a flexible disk cassette that allows its flexible disk to be sufficiently stable in operation to be able to provide increased data storage capacities.
Yet another object of the present invention is to provide a flexible disk cassette that will stabilize disk movement transverse to the mean plane of flexible disk rotation at the head/medium interface where the head or heads and the rotating disk interface with one another to effect data recording and/or playback.
Yet an additional object of the present invention is to provide a flexible disk cassette that reduces fluttering in the area or areas at which the rotating disk and head or heads interact with one another.
Another object of the present invention is to provide a flexible disk cassette in which means for enhancing the cleaning function of a liner located within a disk cassette will also aid in stabilizing the disk.
An additional object of the present invention is to provide a flexible disk, such as a magnetic disk, that includes a hub or center plate and connection thereto which allows the disk to be rotated at high speeds, while remaining stabilized.
Yet another object of the present invention is to provide a method of securing a flexible disk to a center plate or hub that is simple, economical and effects an accurate positioning of the disk on the plate.
Yet a further object of the present invention is to provide a method of making a flexible disk cassette which method results in a realization of the foregoing objects.